This section is intended to provide a background or context to the exemplary embodiments of the invention. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section.
Enhancements to mobile communication systems are currently being investigated to improve the experience of mobile users who use those systems in densely populated areas. In particular, mobile operators have responded to user demands in densely populated urban areas by deploying more access points and by adding or expanding existing coverage areas. Access points are typically evolved node base stations (eNBs), or remote radio heads (RRHs), as specified in the Long Term Evolution Advanced (LTE-A). Coverage areas are defined in terms of the traditional cellular concept of a macrocell, which is a combined geographic area divided into three 120° areas of a circle and a radius of several kilometers. Coverage areas can further be defined by delineating each sector into individual cells such as a single smaller macro cell, two or more micro cells, or a plurality of femto or pico cells, depending on the geographic area, known obstructions and population density.
Conventional cellular networks such as LTE and LTE-A include the concept of a self organizing network (SON) which is an automated function of mounting, configuring and maintaining eNBs in a wireless communication system to lower operating and maintenance costs. One of the functionalities of SON is the automatic allocation of a physical layer cell identity (PCI). In both LTE and LTE-A, a newly added eNB into a communication network is required to allocate a unique PCI for each cell supported by the eNB to avoid interference among neighboring cells. This information is provided to the user equipment (UE) by transmitting a primary synchronization signal (PSS), a secondary synchronization signal (SSS).
There are 504 unique PCIs in LTE/LTE-A grouped into 168 physical layer cell identity groups (PCIG) (0-167), each containing 3 physical layer cell identities (PCI) (0-2). The combination of the PCIG and PCID determines the PCI of a LTE/LTE-A cell. PCID (0-2) is encoded in the PSS while the PCIG (0-167) is encoded in the SSS.
LTE/LTE-A frames contain reference signals (RS) which the UEs use to determine signal attenuation, timing adjustment and handover candidates. A RS is arranged in a specific pattern within the LTE/LTE-A resource block (RB). There are six possible patterns for the reference signals which are determined by the above described PCIG and PCID combination.
Conventionally, two automatic PCI allocation methods employing the SON method predominate, a centralized method and a distributed method. As shown in FIG. 1, the conventional centralized method employs one or more centralized operations and maintenance (OAM) function entities 24 within the element management system (EMS) 20. Each OAM function obtains PCI values from a PCI database 22. In the centralized method, during the initial configuration performed by the eNB, the OAM provides the eNB of specific PCI values which it may employ as the PCI of a new cell. Alternatively, according to the distributed method, the OAM function entity provides the eNB of a usable PCI value list. If the OAM function entity 24 does not provide a usable PCI value list then the eNB assumed a default range from which the eNB will select a PCI value). For example, as shown in FIG. 1, an eNB 60 can receive PCI values 32 transmitted from the OAM function entity 24 which obtains PCI values from a PCI database 22 within the core network 20. The eNB can determine whether neighboring cells contain similar PCI values by maintaining a neighbor relation table 34. The eNB 60 allocates PCI values to cell identifier within the Primary and Secondary Synchronization Signals used for further communicates with user equipment 50 via radio module 36.